Cross guide coupler having a coupling aperture bridged



March 17, 1964 CROSS GUIDE COUPLER HAVING A COUPLING R. H- ANDERSON APERTURE BRIDGED BY A DIAGONAL COUPLING BAR Filed July 21, 1961 ROBERT H. A MlDE/PSO/V BYmJ/ W INVENTOR United States Patent Cambridge, Mass, assignor to a corporation This invention relates generally to directional coupler devices and, more particularly, to novel coupling means for use in a cross guide coupler to provide improved coupling and directivity characteristics.

Directional couplers generally consist of a first or main electromagnetic wave transmission line and a second auxiliary electromagnetic transmission line, said transmission lines being coupled together at a point, or points, so that a wave traveling in the main transmission line is coupled entirely or partially from the main line to the auxiliary line so that it is delivered in a particular desired direction in the auxiliary line. In conventional systems of this nature, if two signal channels, such as waveguides, are suitably coupled together, for example, by being placed at right angles to each other with common openings appropriately positioned in their adjacent walls, a sample of the energy which is being propagated in a first of the guides will be coupled through said openings and be propagated in the second guide in substantially one direction only. The directivity of such a directional coupler is a measure of the power that is propagated in the substantially one direction of said guide to the power propagated in the opposite direction of said second guide. The coupling of the directional coupler is a measure of the power that is propagated in the substantially one direction of the second waveguide to the power which is being propagated in the first waveguide. This invention discloses a structure whereby the coupling of the directional coupler is substantially improved over that available in couplers that are presently known in the art.

In general, the invention utilizes a structure such that the first and second waveguides have a common opening across which there is placed a conductive member, such as a metallic rod, said member being positioned at a selected angle with respect to the direction of propagation of the energy in said first waveguide. More specifically, in a preferred embodiment of the invention the waveguides have a common hexagonal opening with the conductive rod being attached to opposite corners of the hexagonal opening in a direction which is substantially 45 with respect to the direction of propagation of the electromagnetic energy in the first waveguide.

By this construction the coupling may be improved to such an extent that substantially all of the input power to the first Waveguide may be coupled to the second waveguide with a high degree of directivity. With a specific preferred embodiment of the invention, which will be hereinafter described in more detail, it has been possible to construct a directional coupler in which a coupling value, substantially lower than the or 6 db values available with presently known devices, has been achieved, while at the same time suitable directivity values are also obtained. In order to understand more readily the construction and operation of the invention, reference is made to the accompanying drawing wherein:

FIG. 1 shows an exploded, perspective view of a cross guide coupler representing a preferred embodiment of the invention;

FIG. 2 shows a plan view of the coupling element with relation to the waveguides of the embodiment shown in FIG. 1;

FIG. 3 shows a vertical cross sectional view of the 3,125,731 Patented Mar. 17, 1964 coupling element and waveguides utilized in the embodiment shown in FIGS. 1 and 2; and

FIG. 4 shows a plan view of an alternative embodiment of the coupling element of the invention.

In FIG. 1 there is shown a directional coupler 30 comprising a first waveguide 16, a second waveguide 11 and a coupling element 12. Waveguides 10 and 11 are positioned at angles of substantially 90 with respect to each other and a first arrow 13 shows the direction of an electromagnetic wave traveling in a direction designated as P, in waveguide 1'0 as can be seen in FIGS. 1 and 2. The

' opposite end of waveguide 10 is designated by arrow 14 as P For optimum directional coupler operation the electromagnetic wave energy entering from P should be coupled by means of coupling element 12 into waveguide 11 so that it travels in a direction P shown by arrow 15, it being desired that substantially none or" the wave traveling in waveguide it) be caused to propagate in the direction P of waveguide 10 and also that substantially none of the wave coupled into waveguide 11 be coupled in the direction designated as P by arrow 16.

A measure of the coupling C of the cross guide coupler shown in FIGS. 13 is determined by the ratio of the input power, represented as P;, to the coupled power,

A measure of the directivity D of the cross guide coupler shown in FIGS. 1-3 is determined by the ratio of the coupled power, represented by P to the oppositely directed power in waveguide 11, represented by P This value can be measured in decibels in accordance with the formula:

P D 10 log (2) It is clear that for the greatest amount of coupling it is desirable that the value of C in db of Formula 1 be as small as possible. It is also clear that for the best directivity characteristic it is desirable that the value of D in db of Formula 2 be as large as possible.

In one specific embodiment of the invention, which will be herein described, the coupler is designed to provide a coupling value C of approximately 3 db, said value representing substantially improved coupling over that previously available to those in the art. As shown in FIGS. 1-3 the coupling element 12 is fabricated as a separate unit and appropriately soldered to Waveguides 1i) and 11. Waveguide it) has an opening 17 located in a broad side 25 thereof and waveguide 11 has a corresponding opening 31 (partially shown) located in a broad side 26 thereof. Coupling element 12 has a first pair of oppositely disposed flanges 13 which allow the coupling element to fit snugly over opening 17 of waveguide 10 as shown more clearly in FIG. 3. Coupling element 12 has similar oppositely disposed flanges 19 which allow the coupling element to fit snugly over the corresponding opening in perpendicular waveguide 11. The coupling element may thereby be soldered, or otherwise appropriately attached, along the abutting edges common to the element and to the waveguides so as to form a permanent structure.

The coupling element in this specific embodiment has an elongated hexagonal opening 211, said opening thereby being common to both waveguides 10 and 11 and having two parallel sides 32 and 33 substantially longer than the other sides thereof as shown. A cylindrical conductive member, or rod 21, is positioned within said hexagonal opening 213 so as to extend from a first corner 22 to a second oppositely disposed corner 23 of the hexagonal opening. Cylindrical rod 21 is wedge shaped at its ends so as to fit snugly into corners 22 and 23 where it can be attached as by soldering or other suitable means.

When the structure is assembled and soldered as a permanent unit, power entering waveguide at P is coupled through hexagonal opening it) into waveguide 11 in a direction represented by P For the particular structure shown, the waveguides have a broad internal dimension a, as shown in FIG. 3. In one successful embodiment of the invention, the length l of opening 2%) from corner 22 to corner 23 is approximately 1.13:1 and the width w from one to the other of parallel sides 25 and 26 shown in FIG. 2 is approximately 0.70s. The thickness t of coupling element 12, as shown most clearly in FIG. 3, is approximately 0.0541 and the diameter of the cylindrical conductive member, or rod 21, is equal to approximately 0.10:1. It has been found that for these dimensions the coupling C is approximately 3.5 db and the directivity D is approximately 13.5 db.

An alternative embodiment of the invention is shown in FIG. 4 wherein an opening 34 is substantially rectangular in shape and has a conductive rod 35 extending from diagonally opposite corners as and 37 thereof. in one specific embodiment utilizing this configuration shown in FIG. 4, the rectangular opening is a square having lateral dimensions equal to approximately 078a. The cylindrical rod has a diameter of approximately 0.12561 and the coupling element has a thickness of approximately 020a. For these specific dimensions, the coupling C is equal to about 3.0 db and the directivity D is equal to about 10.8 db.

As shown in the plan views of FIGS. 2 and 4 conductive rod 20 is positioned so as to be approximately with respect to the direction of propagation of the input wave P, as shown therein. As this angle is changed the amount of coupling is changed accordingly, it having been found that maximum coupling is obtained at substantially 45.

The preferred embodiments shown in FIGS. 14 and the specific dimensions expressed above do not necessarily represent the only embodiments of the invention. For example, the structure shown in FIG. 3 may be made as a single, integral unit so that waveguides l0 and ill have a common side at the coupling region, said common side having an opening such as that shown in coupling element 12.

Moreover, the dimensions shown in the figure and discussed above may be varied in accordance with the particular application desired. Those dimensions, the values of which may be changed to provide variable coupling and/or variable directivity, involve the thickness t of coupling element 12, the width w of opening 2%, and the diameter of cylindrical member 21.

Generally, as the thickness t is decreased, the value of the coupling C in db decreases and the directivity D in db generally decreases. If the width w is increased, for example, from about 0.3a to 0.70:, the coupling C in db generally decreases, while the directivity D in db generally has a maximum value between about 0.5a and 0.6a.

Moreover, with respect to the width w it has been found that changes in this dimension bring about changes in the impedance matching of the directional coupler system to the input wave. The impedance match of the directional coupler provides an indication of the amount of reflection of an input wave traveling in the direction denoted by the arrow P that would occur when the input wave encounters the coupling unit. It is desirable to maintain a minimum amount of reflection due to the coupling element so that a substantially low voltage standing wave ratio is obtained as measured at the input opening to Waveguide 10. It has been found that the width w of opening 20 can be adjusted to provide a good impedance match so that Such reflections may be reduced 4 to a minimum for values of w of approximately 0.5a to 0.6a.

As the diameter of the cylindrical member increases, the value in db of the coupling C generally decreases while that of the directivity D tends to increase. Since these dimensional changes tend to interact one with the other, the adjustments of each of the dimensions may be performed empirically to achieve the desired coupling and directivity values for a particular application.

The particular embodiments of the invention shown and described herein should not be considered to represent the only embodiments of the invention as variations of the structure, in accordance with the description contained herein, will occur to those skilled in the art within the scope of this invention. For example, as mentioned above, the exact configuration of the opening 20 may in some applications be varied so as to be other than the elongated hexagonal aperture described with reference to FIGS. 1-3 or the rectangular opening shown in FIG. 4. Other geometrical shapes may also occur to those in the art. Moreover, it may be desirable to remove any sharp corners from the coupling structure by rounding the edges thereof where desired. Hence, the invention is not to be construed as limited to the particular embodiment shown and described herein except as defined by the appended claims.

What is claimed is:

1. In combination, a first means for propagating electromagnetic Wave energy; a second means for propagating electromagnetic wave energy in a direction transverse to the direction of propagation in said first means; means for coupling at least a portion of an electromagnetic energy wave in said first propagating means to said second propagating means, said coupling means having an opening therein common to both of said propagating means; a conductive member extending across said common opening at a selected angle with respect to the direction of propagation of said electromagnetic energy wave in said first propagating means.

2. In combination, a first waveguide for propagating electromagnetic wave energy; a second waveguide for propagating electromagnetic wave energy positioned adjacent to and substantially at a right angle with said first Waveguide to provide a region common to said first and second waveguides, a coupling element being positioned at said common region and having an opening common to both of said waveguides, a conductive member extending across said common opening at a selected angle with respect to the direction of propagation of an electromagnetic energy wave in said first waveguide.

3. In combination, a first Waveguide for propagating electromagnetic wave energy; a second waveguide for propagating electromagnetic wave energy positioned adjacent to and substantially at a right angle with said first waveguide to provide a region common to said first and second waveguides, a coupling element being positioned at said common region and having a hexagonal opening common to both of said waveguides, a conductive member extending across said opening from oppositely disposed corners thereof at a selected angle with res ect to the direction of propagation of an electromagnetic energy wave in said first waveguide.

4. In combination, a first waveguide for propagating electromagnetic wave energy; a second waveguide for propagating electromagnetic wave energy positioned adjacent to and substantially at a right angle with said first waveguide to provide a region common to said first and second waveguides; a coupling element being positioned at said common region and having a hexagonal opening common to both of said waveguides; a cylindrical conductive rod extending across said opening from oppositely disposed corners thereof at a selected angle with respect to the direction of propagation of an electromagnetic energy wave in said first waveguide.

5. In combination, a first waveguide for propagating electromagnetic wave energy; a second waveguide for propagating electromagnetic wave energy positioned adjacent to and substantially at a right angle with said first waveguide to provide a region common to said first and second Waveguides; a coupling element being positioned at said common region and having a rectangular opening common to both of said waveguides; a cylindrical conductive rod extending across said opening from oppositely disposed corners thereof at a selected angle with respect to the direction of propagation of an electromagnetic energy Wave in said first waveguide.

6. In combination, a first Waveguide for propagating electromagnetic wave energy; a second waveguide for propagating electromagnetic Wave energy positioned adjacent to and substantialy at a right angle with said first waveguide to provide a region common to said first and second waveguides, a coupling element being positioned at said common region and having a hexagonal opening common to both of said Waveguides, two parallel sides of said hexagonal opening being longer than the other sides thereof, a cylindrical conductive rod extending across said opening from oppositely disposed corners thereof at a selected angle with respect to the direction of propagation of an electromagnetic energy wave in said first Waveguide.

7. In combination, a first waveguide for propagating electromagnetic wave energy; a second waveguide for propagating electromagnetic wave energy positioned adjacent to and substantially at a right angle with said first waveguide to provide a region common to said first and second waveguides, a coupling element being positioned at said common region and having a hexagonal opening common to both of said Waveguides, two parallel sides of said hexagonal opening being substantially longer than the other sides thereof, a cylindrical conductive rod extending across said opening from oppositely disposed corners thereof at substantially a angle With respect to the direction of propagation of an electromagnetic energy wave in said first waveguide.

8. In combination, a first waveguide for propagating electromagnetic wave energy; a second waveguide for propagating electromagnetic wave energy positioned adjacent to and substantially at a right angle with said first waveguide to provide a region common to said first and second Waveguides, said waveguides each having a broad internal dimension a, a coupling element being positioned at said common region and having a hexagonal opening common to both of said waveguides, two parallel sides of said hexagonal opening being longer than the other sides thereof, a cylindrical conductive rod having a diameter of approximately 0.1a and extending across said opening from oppositely disposed corners thereof at substantially a 45 angle with respect to the direction of propagation of an electromagnetic energy wave in said first waveguide, the Width of said opening between said parallel sides being approximately equal to 0.511, the length of said opening from said oppositely disposed corners being approximately equal to 1.25a.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN COMBINATION, A FIRST MEANS FOR PROPAGATING ELECTROMAGNETIC WAVE ENERGY; A SECOND MEANS FOR PROPAGATING ELECTROMAGNETIC WAVE ENERGY IN A DIRECTION TRANSVERSE TO THE DIRECTION OF PROPAGATION IN SAID FIRST MEANS; MEANS FOR COUPLING AT LEAST A PORTION OF AN ELECTROMAGNETIC ENERGY WAVE IN SAID FIRST PROPAGATING MEANS TO SAID SECOND PROPAGATING MEANS, SAID COUPLING MEANS HAVING AN OPENING THEREIN COMMON TO BOTH OF SAID PROPAGATING MEANS; A CONDUCTIVE MEMBER EXTENDING ACROSS SAID COMMON OPENING AT A SELECTED ANGLE WITH RESPECT TO THE DIRECTION OF PROPAGATION OF SAID ELECTROMAGNETIC ENERGY WAVE IN SAID FIRST PROPAGATING MEANS. 